Flexible pretensioned reinforcement for prestressed structures



April 6, 1954 M. CHALOS 2,674,115

FLEXIBLE PRETENSIONED REINFORCEMENT FOR PRESTRESSED STRUCTURES Filed June 9. 1950 3 Sheets-s l e/afar MQFCE/ 524/0; 5 I

fifformr April 6, 1954 M. CHALOS FLEXIBLE PRETENSIONED REINFORCEMENT FOR PRESTRESSED STRUCTURES Filei June 9, 1950 3 Sheets-Sheet 2 &

[w en fW A #0 may MarcE/ C M. CHALOS FLEXIBLE PRETENSIONED REINFORCEMENT April 6, 1954 FOR PRESTRESSED STRUCTURES 3 Sheets-Sheet 3 Filed June 9, 1950 Im/en for Marc6/ Chg {0s 5m A7f01776y Patented Apr. 6, i954 FLEXIBLE PRETENSIONED REINFORCE- MENT FOR PRESTRESSED STRUCTURES Marcel Chalos, Paris, France, assignor to Societe des Grands Travaux de Marseille, Societe Anonyme, Paris, France Application June 9, i950, Serial No. 167,148 7 Claims priority, application France June .23, 1949 Reinforcements are already known which are intended to remain embedded in the concrete with a view to pre-stress the same and which comprise a tensionally stressed part and a compressively stressed part; the latter is surrounded and supported by the former and can be disengaged from the same, with the result that once the concrete in which the outer part is embedded has hardened it is pre-stressed by the said tensionally stressed part.

In a Patent No. 2,449,276 issued September 14, 1948 to Marcel Chalos for: Pretensioned Reinforcement" a reinforcement is described the outer portion of which consists of a fluid-tight sheath comprising small cables.

The present invention relates to a reinforcement of the kind just described of which the components are so improved that it can be used generally wherever a flexible reinforcement must be resorted to.

According to the present invention, the sheath consists of cables wound in helices about a tube; the said cables provide the effective portion of the sheath which is subjected to the tensional stresses imposed upon the reinforcement while the tube is subjected to the pressure exerted by the tensioned cables and protects the core from any contact with the concrete newly cast about the reinforcement.

The said cables are arranged in two layers in each of which the individual cables intersect those in the other layer; the number of cables is larger in the inner than in the outer layer in order to account for the difierence in the distances to the axis; the pitch and the overall section in each layer of cables must satisfy the three following conditions:

(a) The moments of the tensional forces with respect to the longitudinal axis of the sheath must balance one another exactly.

(1)) At the intersection of an outer cable portion with an inner cable portion those peripheral wires of both cable portions which contact each other should run in parallel directions to prevent the wires of one cable portion from being sheared by those of the registering cable portion.

Where the reinforcement is intended to be reeled up in the stressed state the pitch of the outer layer must be so short that the curvature of any cable in said layer shall not change sign in the course of the reeling process.

The tube according to the invention consists of a pair of flexible sheet metal bands wound in overlapping helices; the outer band is formed .with lugs spaced according to the pitch at which Z Claims. (01. 72--50) the cables are to be wound on the tube between these lugs. The latter may be formed by stamp.- ing and bending the band with a press.

The inner metal band is coiled into a tube just the same as the outer band and may be connected therewith, for example by spot welding; the turns of the metal band providing the inner tube are offset with respect ,to those providing the outer tube, for example an amount equal to half their pitch; the provision of such an inner tube contributes to the strength of the whole structure and to the sealing of the joints between the successive turns of the outer tube notably opposite the lugs.

The core constitutes the compressively stressed portion of the reinforcement; according to the invention, it is composed of cylindrical hardenedsteel sections connected with and bearing on one another.

The surfaces of engagement between the sections are cylindrical sectors the axes of which are directed at right angles to the longitudinal axis of the reinforcement.

The said sections are smaller in diameter than the inner diameter of the inner tube in order that they can be pulled out easily once they have performed their pre-stressing duty.

With the reinforcement under stress and as a consequence of the manipulations to which the same is subjected (notably the successive reeling up and unreelingof the same) the sections comprising the core may be expected to crowd together in zizzag fashion in view of the play existing therebetween. In such circumstances the radial forces set up could only be resisted by the sheath at the cost of a deformation of the latter.

With a view to compensate the aforementioned effects of such a play, the centers of the cylindrical end bearing surfaces of the sections are offset in each successive section. Owing to this arrangement the reinforcement can be stretched to a practically straight structure.

According to the invention, the junction members consist of concrete blocks formed with an axial bore and having circumferential reinforcing hoops; the end of the sheath is inserted through the one end of said bore, the tube being sealed to the concrete and the cables embedded in the mass of the block. The other end of the bore is formed with an inner thread designed to parallel beams provided with cleats capable of resisting the action of cross bars.

The empty sheath is mounted in position on the bench, the one of the blocks being rested on one of the. cross bars and the other block being caught by anequalizer whichis subjected to the action of a jack rested on the other cross bar. The sheath is then subjected progressively to a tensional stress amounting to about 1.4 times the rated value (for example 70 tonswith a 50-ton reinforcement) With the sheath thus tensioned, the core sec tions and the end piece are introduced into the tube and the screw is tightened as much as necessary to bring their end bearing. surfaces into engagement with one another.

Thereafter the stress exerted by the jacksisw.

released progressively.

The reinforcement thus stressed is then ready for use. he reeled or rolled up, bending in a plane at right-angles to the axes of the cylindricalend bearing surfaces of the coresectionsbeing permitted by the slip that occurs at the joints between core sections and the play provided between theconvolutions of the strips forming the tubes.-

After theconcrete cast about the reinforcement has set, the core. can be pulled out of the tubean'd re-used- A I A reinforcement according to this invention will now be describedmore specifically, reference beinghadto the appended drawings in which:

Figure l is a plan view of a sheet metal band providing a component-part of the sheath.

Figures 2 and 3 are an elevation and alongitudinal section respectively of the sheath partly provided withthe cables.

Figures 4, 5 and 6 are elevational views of a sectional chain providing the core, parts being shown in section.

Figures 7 and 8 area longitudinal and a cross sectional view respectively of a junction member, Fig. 8' being taken approximately on the line 8-8-in Fig. 7.

"Figures 9-and lll'illustrate the armature-stressing bench respectively in plan. view and in ver. tical sectional view taken on line X-X in Fig. 9.

Figure 11- is an explanatory diagram of the stressing process.

The cylindrical tubeprovidingthe support of the cables and the shield. of the core composed of a pair of sheetmetalbands cciled spirallyabout one another. The outer-band (see Fig.1) is made of flexiblesheet metal ineither margin. of which a series of. cuts .2; are punched which define lugs 3 which are :bent. up at. right angles to the surface of the band andwhich keep the cables 4, 5. 6 in position once they; have been coiled in spirals about the tube. The spacing ofv thesaid lugs and also thepitch of the bandmetal spirals are dependent on the pitch of the cable spirals.

The inner bandT is made of'the'same metal as and is equal in breadth with the "outer'band; it iscoiled just'like' the latter, however; in such a manner that it will equally overlap the two abutting margins of any two successive turned the same and bridge the notches left by 'the'bentup lugs. The-two band metal coils are assembled by' spot-welding asshown at Sin Fig. 3, or by a continuous seam or in any other suitable manner.

In the example described and asshow-n in Fig. 2e first layer-of twln-cables-ly-i are: coiled For convenience in transport, it can 4 in right-handed spirals about the flexible tube thus constituted, about which a second layer of single cables are coiled in left-handed spirals.

i'he core of the reinforcement (see Figs. 4, 5, 6) consists of a'chain' composed of loosely assembled a'nd alternatingly male and female cylindrical sections 9 and I0 which are smaller in diameter than the inner diameter of the tube.

Said cylindrical sections are made of hardened steel and they are milled at their ends to providecylindrical ball-and-socket joints ll, l2 the axes of which are directed at right angles to the longitudinal. axis of the chain. It follows that the several sections are slidably movable with respect to one another at the joints therebetween while their longitudinal axes remain in one and the same plane. atright angles to the axes of the cylindrical joint surfaces. Cut in the said plane at either end of each section is a slot 13 for the accommodation of the one end of a tie-plate I4; milled in either end of each tie-plate is an-oblong hole It through which projects a connecting pin l5.

A play is thus provided in the-linkage of the sectional chainwhereby each element of the-latiter is enabled to assume an ofiset position with respect to the adjacent ones as shown in- Fig. 5.

Effectively, in view of the clearance designedly provided between the chain-of sections and the tube, the sections may well beexpectedto' set themselves in zigzag fashion within the tube; It has been found in practice that with sections having a diameter or 4.2 mm; enclosed in a tube having a. diameter of 43.5 mm. for use in a -t-on reinforcement, with a 1.5 mm. clearance between the core and the tube, undulations may occur in the stressed reinforcementin the plane at right angles to theaxes of thecylindrical section end joints amounting to 6-8 mm. and the period of which is twice the length of a section.

. In order to decrease such a clearance in the tensioned' reinforcement, the sections are set out of alignment with the longitudinal axisof the sheath owing to the play of the pins l5 within the oblong holes I6 and to the onsetting of the axes of the cylindrical end bearing surfaces H, 12. In the-example consider'edsuch a clearance is thus reduced to 0.5mm.

The junction elements (see Figs. '7 ands): consist of concrete blocks i! of any desired shape which have circumferential reinforcements l8 and are provided: with: a: central throughbora l9.

Embedded in the concrete at the one: endof the bore are the end 2d of the tube and: the ends of the-cables 4, 5; 6.

Through the opposite end of the blochcanebe inserted a screw- 2 i the threads: of: which coopcrate with a steelv/ireco'il' Zlpartly embedded in the concrete; 1

The reinforcement is designed tn be coiledlin a plane at right angles to the axes of the'cylin' drical end surfaces of the sections.

This means that the said axe inustbe: kept parallel. Now, in order-'to' -setthe reinforcement under tension, it is necessary to tightenthe'screw 2! in the junction block llinto-engagement with the linked core 9; ill-in sucha-=nlanner that'they will engage one another at their end: bearing surfaces at th'e-same time as-they will assume the positions assigned to them withinthe tube as a result of the particular clearance-decreasin'g arrangement described:hereinbeforer Interposed between the end: as the screw'tand the last link-in: the chain of sections; iaa's'pecia'l section 39 of which one end surface 23 i cylindrical while the other one 24 i flat. A the screw is tightened, a torque will consequently be applied about the longitudinal axis of the section that will tend to twist the whole chain of linked sections. Unless special precautions were taken to prevent such a twisting action the reinforcement once tensioned could only be coiled to a warped spiral, which consequence must be avoided.

With this end in view, the end section 39 is provided with a key 25 which is guided by grooves 26 in the steel wire thread, whereby any twisting action on the part of the said end section upon the core is prevented.

The reinforcement is tensioned on a bench composed of a pair of parallel beams 29, 30 provided with cleats 28 capable of resisting the forces transmitted thereto by cross bars 3|, 32.

The empty sheath, namely, the tube with the cables helically wound thereon, is set in position on the bench, the one end block I! resting on the one cross bar 3| while the other end block is caught by an equalizer 34 which is pulled by means of a jack 33 rested on the cross bar '32.

The sheath is thus subjected to a tensional stress amounting to 1.4 times the rated tensional stress.

The variations in the sheath length, depending on the ram tension, are illustrated in Fig. .11 through the line MN.

While the sheath is under tensionthe chain 5), I0 is introduced and the bolt 2| screwed home into the block l1, and then the ram is progressively released. The line NP (Fig. 11) represents the variation in length of the reinforcement according to the invention with the tension applied by the ram 38, P being the zero point of this tension. The elongation MP of the sheath shows the stress value supported by the core, which is equal to PQ.

Thus, the sheath is put under tensional stress during the period of time corresponding to the line NP. During the said period the respective lengths of the core and the sheath undergo no relative variation and no displacement occurs of the one relative to the other. It follows that no friction is created and that the tensional stress to which the sheath is subjected and which is equal to the ordinate P-Q is actually uniform over the entire length of the reinforcement.

Besides, the reinforecement thus stressed is flexible in a plane at right angles to the axes of the cylindrical end bearing surfaces of the sections and can be transported or shipped in a coiled state.

With the sheath thus held in tension by the core, it is embedded in concrete, e. g. in a concrete beam or column. After the concrete has set, the screw 21 is screwed out and the core is r removed.

Of course, the cable-supporting tube may be designed, or the sections linked to one another, or the cables mounted, otherwise than in the manner described without thereby departing from the scope of the invention.

What I claim is:

1. Flexible pretensioned reinforcement for prestressed structures comprising a tensioned element consisting of a tube made of a pair of helically wound metal bands and a plurality of steel wire cables supported by said tube and wound therearound so as to form two helical layers of opposite direction, a compressed element consisting of a chain of contiguous cylindrical steel links the diameter of which is smaller than the inside diameter of said tube, the adjacent end surfaces of said link being alternately convex and concave, and a pair of junction members disposed at the ends of the reinforecement and consisting of internally screw-threaded concrete prisms in which the end portions of said cables are embedded, and bolts screwed into said prisms supporting the thrust of said compressed element,

said bolts being adapted to be unscrewed to trans fer the tension of the tensioned element to the structure t be prestressed.

2. Flexible pretensioned reinforcement for prestressed structures comprising a tensioned element consisting of a flexible tube made of a pair of helically wound metal bands, lugs being formed at paced intervals along the external surface of the outermost of said metal bands, and a plurality of steel wires supported by said tube and wound therearound so as to form two helical layers of opposite direction, the pitches of said helical layers being a function of said lug spacing; a compressed element consisting of a chain of contiguous cylindrical steel links the diameter of which is slightly smaller than the inside diameter of said tube, said links having cylindrical end surfaces the axes of which are perpendicular to the tube axis, the two end surfaces of a same link being respectively concave and convex; and a pair of junction members disposed at the ends of the reinforcement and corn sisting of reinforced concrete prisms in which the end portions of said wires are embedded, said prisms being formed with an axial screw-threaded bore, a steel screw-bolt screwed into said prism and exerting on said compressed member a compression stress equal to the tension of said tensioned element, said bolt being adapted to be unscrewed to release said compressed element to transfer the tension of said tensioned element to the structure to be prestressed.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 81,193 Morse Aug. 18, 1868 1,828,476 Seidman et a1. Oct. 29, 1931 2,378,58 Schorer June 19, 1945 2,417,141 Syfert Mar. 11, 1947 2,449,276 Chalos Sept. 14:, 1948 2,460,524 Morin Feb. 1, 1949 FOREIGN PATENTS Number Country Date 300,377 Germany Sept. 8, 1917 

